GB2282997A

GB2282997A - Rack steering system for motor vehicles

Info

Publication number: GB2282997A
Application number: GB9420356A
Authority: GB
Inventors: Wolfgang Modinger
Original assignee: Daimler Benz AG; Mercedes Benz AG
Current assignee: Daimler Benz AG
Priority date: 1993-10-25
Filing date: 1994-10-10
Publication date: 1995-04-26
Anticipated expiration: 2014-10-10
Also published as: ITRM940689A1; IT1275054B; GB9420356D0; US5613572A; DE4336286C1; FR2711602B1; GB2282997B; ITRM940689A0; FR2711602A1

Abstract

The invention relates to a rack-and-pinion steering system for motor vehicles with internal track rod joints which are offset transversely with respect to the longitudinal axis of the rack and arranged on separate deflection levers which themselves are drive-connected via connecting struts to a central pick-off or the rack.

Description

1 Rack steering system for motor vehicles 2282997 The invention relates to

a rack steering system f or motor vehicles with a guide and support unit displaceably supporting the rack at its end sections and with inner (that is, remote from the wheels) track rod joints offset transversely to the longitudinal axis of the rack, which track rod joints are arranged on the free ends of two deflection levers, which are arranged at both sides on the guide and support unit and are drive-connected to the rack, which deflection levers are pivotable about support pins directed transverse to the longitudinal axis of the rack.

Such a rack steering system is the subject-matter of EP 04 81 622 Al.

The offset arrangement of the inner track rod joints relative to the longitudinal axis of the rack can be necessary or advantageous if a rack steering system has to be arranged under restricted conditions, such as are typically present in the region of the front axle in present-day passenger cars. This applies particularly where the vehicle engine extends in the longitudinal direction between the front wheels. In this case, the rack must usually be arranged under the oil sump or the bottom of the engine. As a rule, however, such a low-level arrangement of the inner track rod joints is not possible or desirable because the necessary free movement between the track rods and the transverse links of the front wheels is not available or kinematically unfavourable positions of the track rods are the result.

The rack steering system known from EP 04 81 622 Al provides for end pieces which are arranged on the rack and which are displaceably guided in associated end parts of the guide and support unit to engage, by means of trunnions or the like arranged on them, in elongated holes of the deflection levers in such a way that a drive connection configured in the manner of a sliding joint is formed between the rack and the deflection levers.

2 Such a design is relatively complicated and of f ers only little freedom with respect to the arrangement of the deflection levers.

The present invention seeks to create a particularly useful construction for a rack steering system of the type specified at the beginning.

According to the present invention there is provided a rack steering system for motor vehicles with a guide and support unit displaceably supporting the rack at its end sections and with inner track rod joints which are offset transverse to the longitudinal axis of the rack and are arranged on the free ends of two deflection levers, which are arranged at both sides on the guide and support unit and are drive-connected to the rack, which deflection levers are pivotable about support pins directed transverse to the longitudinal axis of the rack, wherein the deflection levers are drive-connected to a central tap-off connection of the rack by means of connecting struts hinged at their free ends.

In the rack steering system according to the invention, the deflection levers can be arranged in various ways on the guide and support unit. It is, in particular, possible to arrange the deflection levers on the mutually facing sides of end holding features (for example flanges) for fastening the guide and support unit.

Because, in accordance with a preferred embodiment of the invention, the central tap-off connection, the hinge points of the connecting struts on the central tap-off connection and the connecting joints between the connecting struts and the deflection levers can be fitted in a plane containing the longitudinal axis of the rack, torques acting on the rack relative to its longitudinal axis are completely avoided. The rack steering system of the invention correspondingly retains ease of movement without great complication in the rack support arrangements.

In a particularly useful embodiment of the invention, provision is additionally made for the connecting struts to 3 h- be hinged on the central tap-off connection at a transverse distance f rom the longitudinal axis of the rack in such a way that the virtual extensions of the connecting struts pass through supports, of the rack, arranged on both sides of the central tap-of f connection, on or in the guide and support unit, near the longitudinal axis of the rack. This permits particularly low loading on the rack supports to be achieved.

An embodiment of the invention will now be described by way of example with reference to the drawings, in which:- Fig. 1 shows a partially diagrammatic plan view onto the rack steering system and Fig. 2 shows a sectional diagram corresponding to the section line II-II in Fig. 1.

In the representation of Fig. 1, the rack steering system is in the straight-ahead position.

A rack 2 which interacts in fundamentally known manner with a pinion, which is accommodated in the housing part 3 and can be driven by an input shaft 4, is arranged so that it can be displaced longitudinally in an essentially tubular support and guide unit 1.

The support and guide unit 1 has, at its ends, flanges 5 or the like for fastening to the chassis, or parts connected to it, of the vehicle.

Near the flanges 5, on their mutually facing sides two deflection levers 6 are held, so that they can pivot, by means of supporting bolts 7 on the support and guide unit 1. The supporting bolts 7 are arranged, as shown in Fig. 2, in joint eyes 8 f ormed on the support and guide unit 1 at a transverse distance from the longitudinal axis of the rack 2. These joint eyes 8 have a relatively large axial length b, so that the deflection levers 6, which respectively encompass the support and guide unit 1 in fork fashion and are respectively supported in hinge fashion on both ends of the joint eyes 8 by means of the supporting bolts 7, are offered a correspondingly wide support base.

The outer ends of connecting struts 9 are hinged on the 4 A- free ends of the deflection levers 6 on the side of the rack 2, or of the support and guide unit 1, facing away from the supporting bolts 7. The other ends of the connecting struts 9 are hinge-connected to a central tap-off connection 10 of the rack 2. The deflection levers 6 are therefore positively pivoted about the axes of their supporting bolts 7 when the rack 2 executes a longitudinal displacement.

The hinged connections of the connecting struts 9 to the central tap-off connection 10 and to the deflection levers 6 are arranged in a plane which contains the longitudinal axis of the rack 2. This prevents the connecting struts 9 from exerting a torque on the rack 2 relative to its longitudinal axis because of thrust and tensile forces transmitted by them. Furthermore, the hinged connections of the connecting struts 9 to the central tapoff connection 10 and to the deflection levers 6 are arranged at such distances from the longitudinal axis of the rack 2 that the force lines of action of the connecting struts 9 pass, at small angles to the longitudinal axis of the rack 2, through support sections 11 arranged in the support and guide unit 1 to guide the rack. Because of this, only a small amount of bearing friction can occur during displacement motions of the rack 2.

The inner ends of track rods 12 are hinged onto the free ends of the deflection levers 6 near the outer ends of the connecting struts 9 and these track rods 12 are hingeconnected at their outer ends, in a fundamentally known manner, to steering arms 13 by means of which the vehicle (front) steered wheels 14 are pivoted about essentially vertical axes A during steering manoeuvres. The arrangement is then configured in such a way that the steering arms 13 and the respectively associated deflection levers 6 form a steering quadrilateral acting in the same direction.

As is particularly shown by Fig. 2, oblique setting of the pivoting axes, determined by the supporting bolts 7, of the deflection levers 6, can achieve the effect that even in the case of a low-level arrangement of the rack 2, the inner K I" joints, of the track rods 12, connected to the deflection levers 6 have a relatively high location. There is, correspondingly, a large amount of design freedom with respect to the height location of the track rods 12. In addition, this makes it relatively easy to ensure sufficient freedom between the track rods 12 and the transverse links 15 arranged under them for guiding the steered wheels 14.

Because of the wide support base b of the deflection levers 6 on the respective joint eyes 8, only relatively small support f orces occur even when the track rods 12 execute relatively large angular motions relative to the plane of pivoting of the deflection levers 6 when the suspension of the steered wheels 14 deflects. In particular, suspension movements of the steered wheels 14 cannot exert any torque on the rack 2 relative to its longitudinal axis because the deflection leverz 6 are fitted between the track rods 12 and the connecting struts 9.

Despite its ease of movement, the rack steering system according to the invention has little sensitivity to shock because the steered wheels 14 are effectively disconnected from the rack 2, and therefore also from the steering wheel (not shown), because of the hinged connections of the deflection levers 6 with the connecting struts 9 and the track rods 12.

The possibility of arranging the track rods 12 at a high level even in the case of a low-level arrangement of the rack 2 offers the advantage that relatively long steering arms 13 can be arranged so that the rod forces to be transmitted by the track rods 12 and by the connecting struts 9 are reduced.

6

Claims

CLAIMS 1.

1- 1. A rack steering system for motor vehicles with a guide and support unit displaceably supporting the rack at its end sections and with inner track rod joints which are offset transverse to the longitudinal axis of the rack and are arranged on the free ends of two def lection levers, which are arranged at both sides on the guide and support unit and are drive-connected to the rack, which deflection levers are pivotable about support pins directed transverse to the longitudinal axis of the rack, wherein the deflection levers are drive-connected to a central tap-off connection of the rack by means of connecting struts hinged at their free ends.

2. A rack steering system according to Claim 1, wherein the connecting struts are hinged on the central tap off connection at a transverse distance from the longitudinal axis of the rack in such a way that the lines of action of the rod forces of the connecting struts pass through supports of the rack arranged on both sides of the central tap-off connection, on or in the support and guide unit.

3. A rack steering system according to Claim 1 or 2, wherein the pivot pins of the deflection levers and their connecting hinges with the connecting struts and the track rods are arranged on opposite sides of the longitudinal axis of the rack.

4. A rack steering system according to any one of Claims 1 to 3, wherein the connecting hinges between the deflection levers and the connecting struts and the connecting hinges between the deflection levers and the track rods are at a distance from one another in the peripheral direction with reference to the pivot pin of the deflection levers.

4 4 7

5. A rack steering system according to any one of Claims 1 to 4, wherein the connecting hinges between the connecting struts and the central tap-off connection and between the connecting struts and the deflection levers are located in a plane containing the longitudinal axis of the rack.

6. A rack steering system according to any one of Claims 1 to 5, wherein, viewed in the forward travelling direction of the vehicle, the track rods are arranged in front of the centre of the steered wheels.

7. A rack steering system according to any one of Claims 1 to 5, wherein, viewed in the forward travelling direction of the vehicle, the track rods are arranged behind the centre of the steered wheels.

8. A rack steering system according to any one of Claims 1 to 6, wherein the deflection levers andthe steering arms, which are positively connected to them by means of the track rods and are arranged at the side of the wheels, form steering quadrilaterals acting in the same direction.

9. A rack steering system according to any one of Claims 1 to 5 and 7, wherein the deflection levers and the steering arms, which are positively connected to them by means of track rods and are arranged at the side of the wheels, form steering quadrilaterals acting in opposite directions.

10. A rack steering system for motor vehicles, substantially as described herein with reference to and as illustrated in the accompanying drawings.